In conventional optical fiber-based strain measurement systems, a source signal is directed into an optical fiber and a return signal occurs because of strain imposed in the optical fiber or because of a polarization reconfiguration due to mechanical variations imposed on the optical fiber. The signal to noise ratio for the return signal in such conventional systems is less than optimal because the return signal is much smaller in magnitude than the linear source signal. Bragg gratings can be written into the optical fiber in such systems to produce a larger return signal, but the signal to noise ratio for the return signal remains lower than desired. In addition, the wavelength of the source signal in conventional optical fiber-based strain measurement systems is typically varied across a predetermined range and the return signal is monitored to detect a peak level, with the strain measurement signal corresponding to the wavelength of the source signal when the peak level is detected. This type of system imposes a delay for each measurement corresponding to the time required to sweep the source signal across the range of operating wavelengths.
Accordingly, there is a need for an optical fiber-based strain measurement system having a return signal with a higher signal to noise ratio. In addition, there is a need for an optical fiber-based strain measurement system providing a measurement signal in real-time.